Model-Based Fouling Monitoring Tool for Cracked Gas Compressor in Ethylene Plants

Abstract

Although ethylene plants are well understood, there remain several challenges that ethylene producers are facing. One key problem is fouling in the cracked gas compressor (CGC) train. This complex phenomenon represents a major reliability issue in steam crackers, resulting in reduced performance efficiency, reliability issues and losses of many millions of dollars. This project investigates fouling formation in the CGC and explores a procedure to monitor the performance of the compressor. Fouling formation and propagation was predicted using rigorous modelling of the compressor. A dynamic simulation was used to estimate fouling formation under various process conditions. A detailed simulation of the CGC was made using gPROMS ProcessBuilder. It was found that injection of HP BFW plays a major role in monitoring the CGC system and that varied high injection of HP BFW describes the plant most accurately. Polytropic efficiency was not the most effective approach for fouling monitoring in the selected plant, since the feed slates and the cracking severity are varied. State of the art method was used in order to have a more efficient monitoring system. This was based on the actual power consumption and the theoretical power demand. In addition, fouling factor was defined as an improved key indicator, thus it could be included as the monitored variable in the control system. It was observed that most of the fouling takes place in the CGC stages 1-3. Monitoring aftercoolers however was achieved by comparing the actual pressure drop and the flow-adjusted pressure drop. It was noticed that the CG 1st stage aftercooler gets fouled the most, followed by the CG 2nd stage aftercooler. Monitoring both the CGC and the aftercoolers determines that the CG 1st and 2nd stages has the highest tendency for fouling. The estimated energy savings of 1566 kW could be realized by employing the CGC system monitoring tool. This is equivalent to $ 58,531 per year.